Wireless communication is extensively used in mobile or nomadic applications.
In a typical mobile/nomadic application, a mobile or nomadic wireless device or mobile station will try to establish a link with a fixed base station, so as to transmit information to the base station. To achieve coverage of the desired area, multiple base-stations must be used. FIG. 1 shows an example of a system used to support a mobile application. Mobile station 111 will try to establish a link with one of base stations 121 and 122, as it travels along path 131.
Typical solutions for mobile or nomadic wireless devices use omnidirectional antennas that are isotropic or have similar properties, for example gain, in all directions of interest.
While mobile/nomadic devices use omnidirectional antennas, strict separation between base-stations covering adjacent areas is required to avoid harmful self-interference.
Separation can be achieved through:
Time, that is, the base stations do not transmit and receive at the same time,
Frequency, that is, the base stations transmit and receive on different frequencies, or
Code, that is, the base stations transmit and receive using different codes.
All these methods reduce the total system capacity.
FIG. 2 shows an example of the coverage 403 for base-station 401 and the coverage 404 for the base-station 402 when both base-stations use the same frequency channel, and the three mobile/nomadic devices 406, 407 and 408 use omnidirectional antennas. This assumes there are no other time or code methods used to reduce interference between the two base-stations 401 and 402. As can be seen, much of the area of interest 405 is not adequately covered. Mobile device 406 receives coverage, that is, it can establish an operating link with better than threshold signal quality from base station 401 in area 403. Similarly mobile device 407 receives coverage from base station 402 in area 404. However, mobile device 408 cannot receive coverage from either base station 401 or 402 because the signal quality is not good enough. This is because the omnidirectional antenna captures signals from the two base-stations 401 and 402 and needs to be very close to one of them and very far from the other to obtain the needed signal quality.
In order to solve the problem shown in FIG. 2, there is a need for a system that has omnidirectional coverage, but is able to focus on one sector so as to optimize signal quality to enable communications with the highest reliability. Until now, systems have focused on optimizing signal strength, which may not result in enabling communications with the highest reliability.